Heavy brines are used during many different stages of the oil and gas exploration, drilling and production cycle, particularly as a component of drilling fluids, packer fluids, work-over fluids, kill fluids and completion fluids. Packer fluids are used in the annulus of a well that surrounds the production tubing; work-over fluids are those used during remedial operations of a well; kill fluids are used to suspend a well either temporarily or permanently by hydrostatically over-balancing it with heavy brine; completion fluids are used after a well has been drilled but before the well has been brought online to production.
All applications rely on the same properties of the heavy brines and that is their density. In all instances the density of the fluid is tailored to ensure the hydrostatic head of the column of fluid is higher than that of the reservoir pressure, so as to prevent a blow-out, but not so heavy that the brine is lost to the formation, which can lead to irreparable skin damage. Different brines and mixtures of brines can be used to cater for the different formation pressures, depth of wells and orientation of wells. The lightest brine used is sodium chloride (NaCl) which is 1.2 g/cm3 and the heaviest tends to be zinc bromide (ZnBr2) which is 2.65 g/cm3. Heavy brines are used in drilling and well completion operations and can be is defined as a water containing a high concentration of dissolved inorganic salts. More specifically a heavy brine is defined as a water-based solution of inorganic salts used as a well-control fluid during the completion and work-over phases of well operations. Heavy brines are solids free, containing no particles that might plug or damage a producing formation. In addition, the salts in heavy brine can inhibit undesirable formation reactions such as clay swelling. Brines are typically formulated and prepared for specific conditions, with a range of salts available to achieve densities ranging from 8.4 to over 22 lb/gal (ppg) [1.0 to 2.65 g/cm3] but more commonly from 10 to 18 lb/gal (ppg) [1.2 to 2.2 g/cm3] and even more commonly between 11.5 to over 17 lb/gal (ppg) [1.4 to 2.0 g/cm3]. A brine is considered to be a heavy brine in the sense of this invention it its density is 1.15 g/cm3 or above, more preferably 1.2 g/cm3 or above, still more preferably 1.4 g/cm3 or above. The preferred upper limit of density is 2.65 g/cm3. Preferred ranges of density are 1.2 to 2.65 g/cm3, more preferably 1.4 to 2.2 g/cm3, still more preferably 1.5 to 2.0 g/cm3.
Common salts used in the preparation of simple brine or heavy brine systems may include, but are not limited to, single salts or mixtures of multiple salts comprising sodium chloride, calcium chloride, calcium nitrate and potassium chloride. More complex brine or heavy brine systems may include, but are not limited to, single salts or mixtures of multiple salts comprising calcium bromide, zinc bromide or zinc iodine salts. These complex brines are generally corrosive and costly.
A particular challenge with heavy brines is their corrosivity. This is brought about by a few different features of the heavy brines. Firstly, the heavy brines tend to be saturated with respect to oxygen; secondly the heavy brines are strongly electrolytic and allow for efficient electron transfer and therefore corrosion; finally the heavy brines themselves can be of a very low pH.
There are several patents relevant to the art of corrosion protection for heavy brine systems and these can be classified into sets based on the fundamental chemistries covered in their art.
The first set involves the use of metal salts. U.S. Pat. No. 8,007,689 utilizes metalloids of antimony or germanium. It further discloses a more complex blend of morpholine derivatives, an unsaturated alcohol and an organic acid with at least two of these components together in any given blend. The mechanism is likely to be oxygen scavenging from the reducing agents and also passivation of the metal surface using the metalloids.
U.S. Pat. No. 4,849,171 discloses the use of MgO used as an intensifier with super phosphate being contained in the overall blend. Again this is a passivating mechanism that offers the corrosion control.
U.S. Pat. No. 4,997,583 teaches arsenic salts as the corrosion inhibitor, either alone or in combination with an admixture of urea (as a synergist). Arsenic is As2O3, AsBr3, or NaAs2O5 typically added at 200 ppm (arsenic).
US-2008/0274013 discloses the use of molybdenum oxide, and compounds based on antimony, copper and bismuth. These are used in combination with acetylenic amines or acetylenic alcohols.
EP-0153192 uses mono- and divalent salts of erythorbic acid and gluconate (sodium and iron salts). This can be made in a solid or liquid form. It is co-blended with alkali metals, specifically molybdate salts are added. The mechanism is unclear, but is postulated as scavenging combined with a chelation effect.
This set of patents all use metal salts where the metal component is invariably a very heavy element. Typically this means the metal salts are environmentally hazardous, as they can lead to non-competitive enzyme inhibition. This is a major drawback with these types of solutions as legislation invariably would not allow their use.
The next set of patents is based around the use of sulfur containing compounds.
U.S. Pat. No. 4,536,302 discusses the use of sulfur compounds where the oxidation state is either 0 or >0. Thiocyanate or thio amide is used at concentrations as high as 1 g/L. Furthermore, the reference discloses the addition of a reducing sugar (mono-saccharide, disaccharide or oligosaccharides) such as glucose, fructose, lactose, etc. These sugars are added at even higher rates of 2 to 10 g/L.
U.S. Pat. No. 4,728,446 describes a corrosion inhibitor composition containing an alkali or alkaline-earth metal halide in water, zinc ions and thiocyanate ions.
U.S. Pat. Nos. 4,784,778 and 4,784,779 disclose the use of 2-mercaptoethanol, sodium, ammonia and/or calcium thiocyanate, with or without the addition of aldose based antioxidants such as arabinose, ascorbic acid, isoascorbic acid, gluconic acid etc. Ammonium thioglycolate is also mentioned as an additional component. It is noteworthy that very high concentration of inhibitor is required in the experimental data.
U.S. Pat. No. 4,980,074 discloses the corrosion inhibitor as a blend of soluble aliphatic or aromatic aldehydes with or without olefinic unsaturation in combination with an alkali metal, thiocyanates or ammonium thiocyanates.
EP-0139260 discusses phosphorus containing compounds and the use of phosphonium salts such as triphenylphosphine. This is in combination with thiocyanate as well as a commercial product being added called “TRETOLITE™ KI-86”. “TRETOLITE™ KI-86” is disclosed as a Mannich amine-based formulation.
WO-2009/076258 teaches a bis-quaternized compound for inhibiting corrosion and/or removing hydrocarbonaceaus deposits in oil and gas applications, the compound having a general formula:
    (a) wherein R1, R2, R3 and R4 are independently selected from the group consisting of: an unsubstituted branched, chain, or ring alkyl or alkenyl having from 1 to about 29 carbon atoms in its main chain; a partially or fully substituted branched, chain, or ring alkyl or alkenyl having from 1 to about 29 carbon atoms in its main chain, wherein said substitution includes being oxygenized, sulfurized, and/or phosphorylized; and combinations thereof;    (b) L1 and L2 is each a moiety independently selected from the group consisting of: —H, —CO2H, —SO3H, —PO3H2, —CO2R4, —CONH2, —CONHR4, —CON(R4)2, and combinations thereof; wherein each R4 is independently selected from the group consisting of: branched or unbranched alkyl, aryl, alkylaryl, cycloalkyl, and heteroaromatic groups having from 1 to about 10 carbon atoms, and combinations thereof;    (c) x is from 1 to about 10; and    (d) y is from 1 to about 5,
which may be used together with a phosphate ester and a mercapto synergist.
WO-2012/063055 teaches compositions comprising at least one compound that is a ring-opened derivative of a C5-C21 alkylhydroxyethyl imidazoline and a quaternary ammonium compound. One group of compounds that have been found to be useful are amphoacetates, alkylamidoamineglycinates or amphocarboxyglycinates. Two other groups are di-acetates and amphosulfonates. The ring-opened derivatives of C5-C21 alkylhydroxyethyl imidazolines are disclosed be especially effective when used in combination with alkyl quaternary amines (alkyl quats) and/or alkyl quaternary esteramines (ester quats).
The corrosion caused by heavy brines is fundamentally different to that which occurs during normal production operations when regular brines are used. Regular brines are the subject matter of the WO-2009/076258 and WO-2012/063055 references. Corrosion in normal production operations (such as that described in WO-2009/076258 and WO-2012/063055) involves brines with a density much <1.4 g/cm3 and are anoxic. This type of corrosion is caused by the dissolution of corrosive species, most typically CO2 and H2S.
Heavy brines on the other-hand offer the following unique problems to the oilfield production chemist:                In a first aspect they are highly saturated, often with reactive divalent ions. This poses a solubility problem for any corrosion inhibitor, something not usually encountered in less saturated, regular brines. This also promotes a more pervasive corrosion inhibition mechanism with such aspects as chloride stress corrosion cracking mechanism and also a higher general corrosion rate due to the high conductivity of the solution. The solubility of corrosion inhibitors is made all the more challenging when high levels of calcium, zinc, or bromide are present. Such ions are practically absent from standard oilfield produced waters (such as those detailed in D1 and D3).        In a second aspect, oxygen corrosion will occur. Heavy brines are introduced into well operations from the surface and therefore are fully saturated with respect to oxygen. This is absolutely not the case with production operations where the produced waters are coming from the reservoir and flowing to the surface and therefore are completely anoxic. The presence of oxygen in the heavy brines creates a very severe corrosion environment and specific know-how and chemistry needs to be applied in order to deal with the oxygen present.        
Table of heavy brine density vs. regular oilfield brines (WO-2009/076258 and WO-2012/0630553)
BrineBrine ATable 3NaClCaCl2KClWO-2012/WO-2009/HeavyHeavyHeavyComponent063055076258BrineBrineBrineNaCl74.1318.6793311.265KCl0.710.225252.43MgCl2•6H2O4.211.3284CaCl2•6H2O17.190.8031540.632SrCl2•6H2O0.0578BaCl2•2H2O0.0023NaHCO30.682.5076Na2SO40.020.9067TDS (mg/L)86.22622.527311.265540.632252.430Density (g/cm3)1.0961.0241.1981.3891.162Density (PPG)9.148.541011.69.7
So it can be seen from this table that Brine A (WO-2012/063055) is fairly saline but is still less that even the lightest brine (KCl) used in well service operations and general well work and furthermore are much more complex mixtures resulting from their natural origin in oilfield reservoirs being composed of multiple salt sources of low concentrations.
WO-98/41673 teaches compositions for inhibiting the corrosion of iron and ferrous metals in heavy brines, comprising, as active constituent,
at least one alkyl-poly(ethyleneamino)-imidazoline or 2-alkyl-poly-3-(ethyleneamino)-1,3-diazoline, corresponding to the general formula
    in which    R is a linear or branched, saturated or unsaturated hydrocarbon chain containing 10 to 22 carbon atoms, and in which n is a number from 0 to 3, and at least one mercapto acid corresponding to the general formula
    with    n is 0 to 3,    R1 is H or SH,    R2 and R3 together or independently is C1-C4, CON(R6)(R7) or COOR8,    R4 and R5 together or independently is OH, NH2 or SH when R1≠SH,    R6 and R7 together or independently is H or C1-C4,    R8 is H or C1-C8,    it being possible for R2 to R5 to be included in an aromatic ring when n=1,    A being a COOH, SO3H, OSO3H, POSH or OPO3H acid group,    the molar ratio between the mercapto acid component(s) and the imidazoline component(s) being from 1.0 to 1.5.
In general the mechanism for sulfur containing compounds is one of passivating layer formation and is a very effective means of corrosion control. However there is an increased risk of stress corrosion cracking and several failures in the industry have been attributed to the reliance of sulfur containing compounds alone as effective corrosion control.
Film forming amines have also been discussed in the patent literature, but generally these are considered to be low performance and generally not compatible with a lot of the brine types.
U.S. Pat. No. 4,304,677 describes the use of several different additives for the heavy brines including corrosion inhibitors. Materials included corrosion inhibitors based on triethanol amine, propargyl alcohol, pyridine and its derivatives, the latter of which can be described as an amine-based film-former.
U.S. Pat. No. 4,292,183 discloses the use of commercial inhibitor packages such as “TRETOLITE™ KW-12” and “MAGCOBAR 101” which are described as film-forming amine-based corrosion inhibitor.
Other patents relevant to the art, use other types of chemistry.
U.S. Pat. No. 6,149,834 is not for oilfield use, rather is for inhibiting chloride salts used in de-icing application—relevant in a technical sense. Here the corrosion inhibitor is composed of de-sugared sugar beet molasses where 5 to 25 wt % is applied versus the chloride salt, furthermore small amounts of associated zinc and phosphorus salts were reported as boosting performance.
U.S. Pat. No. 4,046,197 names a commercial product (Corexit 7720) used in conjunction with a delivery system for a salt suspension.
WO-2000/039359 discloses the use of chelating agents such as 2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC) and hydroxyphosphone-acetic acid (HPA) with phosphonocarboxylic acid (POCA). Azoles are also added such as mercapto benzotriazoles (MBT), benzotriazoles (BT), tolyltriazoles, etc.
Corrosion inhibitors for protection while using stimulation acids are also relevant because there are similarities in the arts when compared to heavy brine inhibitors.
US-2006/0264335 discloses the use of terpenes as intensifiers, for example carotene, limonene, camphor, menthol, etc.
U.S. Pat. No. 6,511,613 uses propargyl alcohol as the main inhibitor with iodine containing compounds as an intensifier. This is perhaps the most commonly used method in the art of protection against acidic corrosion inhibition.
U.S. Pat. No. 5,976,416 discusses a more classic approach, for organic acid corrosion inhibition, where quaternary ammonium salts and activators are combined with thioglycolic acid and thiosulfates.
U.S. Pat. No. 6,192,987 discloses the use of one or more acetylenic alcohols and hexamethylene-tetra-amine.
The intention of the current invention is to deliver new corrosion inhibitor formulations that lower the corrosion rates to negligible levels in heavy brine fluids. A corrosion rate may be considered to be negligible if it is <4 milli-inches per year, hereinafter mpy. It is further, an object of the present invention to provide much higher performance than the existing art. It is further, an object of the present invention to be applicable and compatible in all oil industry used heavy brine types including calcium nitrate which is often not specifically mentioned in the art. It is further, an object of the present invention to provide a product that can function efficiently and to the desired level of corrosion control without the addition of an oxygen scavenging, or reducing agent. It is further, an object of the current invention to provide corrosion protection particularly at high temperature, as well as low temperature performance, due to the trend to drill deeper, hotter, higher pressure wells. It is further, an object of the present invention to provide a corrosion inhibitor that is composed completely of organic based components with no salts or inorganic components, and especially no heavy metals, therefore providing an environmentally acceptable corrosion inhibitor package. It is further another object of the present invention to provide a corrosion inhibitor that does not induce, or contribute to in any way, risk of stress corrosion cracking. Yet another objective of the present invention is to prepare a corrosion inhibitor package composed of several ingredients and combination of ingredients to allow flexibility and therefore a more ubiquitous use around the world given the different legislations in place. Still another object of the present invention is to provide a formulation that kinetically reduces the corrosion rate much faster than any other products described in the art.
These and other objectives of the present invention are described in more detail within this Application and will be described below.